Catalyst deactivation is a common problem encountered in the use of heterogeneous catalysts and may be due to poisoning, sintering, metal fouling or deposition of carbonaceous materials on the surface of the catalyst ("coking"). Some catalyst deactivation processes, such as sintering, are essentially irreversible and the affected catalyst must be replaced. Other deactivation processes, such as coking, are partially or completely reversible and the service life of the catalyst can be significantly extended by the proper choice of regeneration methods and conditions.
Unfortunately, there is no "universal" method of catalyst regeneration. Both the cause of catalyst deactivation and the nature of the catalyst itself (composition, preparation history, etc.) must be considered in choosing a regeneration method.
Catalysis of the methanol dissociation reaction, or the related methyl formate dissociation reaction, to produce hydrogen and CO is of current interest as a route to "clean" fuel from an easily stored, readily available source. Copper-based catalysts are generally more active than non-copper containing catalysts in methanol dissociation reactions. However, these copper-containing catalysts gradually deactivate at a rate which depends both on the catalyst composition and the reaction conditions.
"Coke", a common cause of catalyst deactivation, can usually be removed by heating the deactivated catalyst in an oxidizing atmosphere until oxidation or "burn-off" of the coke is complete. However, the optimum conditions for regeneration are dependent on the nature of the particular catalyst. For example, the rate at which the carbon deposits are removed as CO or CO.sub.2 generally increases with temperature, but above a critical temperature (which is determined by the catalyst), the catalyst may sinter, with dramatic loss of catalytic activity.